Views

Look again at the left column of the
Schema Browser. You already know what a table is - a storehouse for
data of the same type. But what about those other terms?

A view is a virtual table created by combining records from
real tables. The records that make up a view remain in their original
tables, but they can be accessed and searched through the view.

What does this mean for you? If you're a database programmer, the difference
is crucial. For the rest of you, the difference is... nothing. For the
purpose of searching for data, a view is a table, and a table is a view.
You can search views just like tables, by listing them in the from block.

In fact, many of the so-called "tables" you have been using are actually
views! The specObj "table" is actually a view created from the specObjAll table,
which contains both good and bad spectra. The PhotoPrimary, Star, Galaxy,
and Unknown databases are all views created from the PhotoObjAll table.
You've been using these views all along!

Try searching the same area of sky using the SpecObjAll table and
the SpecObj view, or the PhotoObjAll table and Star, Galaxy, or Unknown
views. What differences do you see?

One particularly important view is the SpecPhoto view, which contains photometric
and spectroscopic information on the same objects. Using SpecPhoto is just like doing a join
between SpecObj and PhotoObj, but SpecPhoto is easier to use, and your queries will run
faster.

When you are ready to move on, click Next to learn about functions.

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